Interfacial modification of hybrid lead halide perovskite solar cells using Fe2O3/WO3 electron transport bilayer for enhanced efficiency and stability

• Solution-processed Fe 2 O 3 /WO 3 bilayer ETL establishes graded band alignment and enhances electron extraction. • DIPAI surface passivation reduces surface traps and promotes lateral grain growth. • Optimized devices achieve a champion PCE of 18.38% (J SC 22.50 mA·cm -2 , V OC 1.14 V, FF 71.82%). • Bilayer and DIPAI devices retain ∼84.8% of initial PCE under accelerated ambient aging and use low-temperature, scalable processing. In this work, we report an integrated interfacial engineering strategy for high-performance, stable hybrid lead halide perovskite solar cells (PSCs) using an Fe 2 O 3 /WO 3 electron-transport bilayer combined with an interfacial layer (IL) of di-isopropylammonium iodide for surface passivation. The bilayer pairs chemically robust Fe 2 O 3 at the transparent electrode with a WO 3 top layer to produce graded conduction-band alignment, enhanced electron extraction, and UV-resistant hole blocking. Post-deposition IL treatment passivates under-coordinated Pb 2+ sites and reduces surface roughness, leading to improved interfacial quality. The optimized Fe 2 O 3 /WO 3 with IL devices achieved a power-conversion efficiency of 18.38% (J SC = 22.50 mA.cm -2 , V OC = 1.14 V, FF = 71.82%) and exhibits improved reproducibility versus controls. The optimal device retained ∼ 84.8% of initial PCE, outperforming Fe 2 O 3 or WO 3 -only devices. Our results demonstrate that synergistic bilayer ETL engineering combined with molecular surface passivation simultaneously mitigates interfacial recombination and environmental degradation, providing a scalable, low-temperature route to durable, perovskite photovoltaics.